The .221 Fireball has been used by
wildcatters to create a small efficient .17 caliber cartridge. The most common is the
.17 Mach IV which is essentially the .221 necked down to the smaller caliber. This cartridge is reported to have a very flat trajectory and to be relatively quiet with low recoil. It has been so popular as a wildcat that in 2007 Remington legitimized it by introducing their version only slightly different from the Mach IV and calling it the
.17 Remington Fireball. A .20 caliber version is also gaining popularity called the
.20 VarTarg (VT), "vartarg" being the combination of the words "
varmint" and "
target". The .221 Fireball has also been used as the base for the
.300 Whisper, sometimes referred to as the .300/.221 or .300 Fireball. It is also the basis for other cartridges in J.D. Jones' Whisper family including the 6 mm Whisper, which has been adopted by
Knight's Armament Corporation for their
Knight's Armament Company PDW as the 6×35mm PDW. == Gallery ==